Mechanical deformation of a liquid crystal diffraction grating in an elastic polymer

We demonstrate the tuning of the diffraction efficiency in a polymer-dispersed liquid crystal (PDLC) diffraction grating by mechanical shear deformation. We chose a photocurable thermoset with elastic mechanical properties as the host material to demonstrate the tuning effect. Raman–Nath gratings were prepared by anisotropically curing a mixture of commercial photopolymer doped with liquid crystal. The mixture was contained between glass slides which were mounted in a simple shearing device. During the photopolymerization, the liquid crystal phase separated into 2-μm droplets organized into channels with 3.8-μm spacing. Gratings were deformed by shearing the samples in a direction perpendicular to the channel orientation. The diffraction intensity and morphology were monitored as a function of shear strain. Reversible tuning was observed due to the elastic nature of the matrix. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 523–526, 1998     

Behavior of phenolic antioxidants in a partitioned medium: Focus on linoleic acid peroxidation induced by iron/ascorbic acid system

The peroxidation of linoleic acid was induced by the Fe²⁺/ascorbic acid system in a micellar medium, and the kinetics of the produced conjugated dienes to a weak level (0.7 μM) in order to initiate only the sequential oxidative reactions without superimposed antioxidant activity. Other conditions were established to obtain a simple kinetic profile. With a linoleic acid/Fe²⁺ ratio of 10 and an Fe²/ascorbic acid ratio of 23 in the medium emulsified by Tween and saturated in oxygen, no limiting effect of substrates was observed for several hours. Fe²⁺ disappeared in less than 5 min, while a linear propagation rate was reached after 1 h for up to 15 h. Two parameters were chosen to quantify the level of the oxidation: the slope of the linear phase, and the extrapolated absorbance of this step at zero time. These two parameters were used in order to compare the antioxidant power of different phenolic compounds in this partitioned medium.